NOT financial advice - seek advice from a professional for your specific situation

    TaxKilnUK tax guidance

    Audit triggers cluster

    HMRC audit triggers — by regime and by trade

    An audit trigger is anything in your filing — or in third-party data HMRC already holds — that pushes you up the queue for an enquiry, nudge letter, or compliance check. HMRC increasingly works from rather than random sampling: Connect cross-references banks, Companies House, Land Registry, employer payroll and platform reports against what you declared. This hub indexes the trigger material already documented across TaxKiln — by regime, and by trade — so you can see where you sit before HMRC does.

    Last reviewed:

    Guidance, not advice. We explain the rules, we don't assess your situation. Always seek financial or tax advice from your accountant, or contact HMRC. Read our editorial scope →

    Nothing on this page is new tax guidance. Every entry points to an existing TaxKiln page (with its own statute citations + worked examples) or to a dated, statute-grounded fact. If a topic has no dedicated page yet, it is linked to the closest existing treatment rather than padded out.

    Self Assessment: late filing, late payment, payments on account

    The single largest source of automatic HMRC contact. Late-filing penalties and payments-on-account surprises are formulaic — they fire from the SA system itself, not from a human reviewing your file.

    Digital platform reporting (from 1 January 2024)

    Marketplaces and gig platforms now report seller-level income directly to HMRC under the UK's implementation of the OECD model rules. If your declared income doesn't match the platform's annual return, that is now a live trigger — not a theoretical one.

    MTD ITSA (from 6 April 2026)

    Quarterly digital submissions over the threshold create four new trigger points per year per trade — late or missing quarterly updates feed into a points-based penalty regime that didn't exist before.

    Residence + non-dom reform (from 6 April 2025)

    The remittance basis was abolished and replaced with the 4-year FIG regime; IHT moved from domicile to a long-term-resident (LTR) test. Anyone with a cross-border footprint is now sitting on a much bigger trigger surface than they were a year ago.

    Once HMRC has opened a check: enquiries, statutory review, FTT

    If you are past the trigger and into a live check, the procedural framework matters more than the underlying tax. These pages cover the route from enquiry letter to First-tier Tribunal and the disclosure-facility alternatives.

    Trade-specific triggers

    Each TaxKiln trade page carries its own commonAuditTriggers list — the patterns that draw HMRC attention to that specific cohort. Aggregated below from 22 trade guides. Follow the link for the full guide (allowable expenses, vehicle treatment, capital allowances, worked example).

    Tax for beauty businesses

    • Cash tips + cash payments not declared
    • Chair/room-renter mis-classification (salon owner risk: back PAYE + Employer NI)
    • Family member on payroll without genuine duties
    • Retail product stock taken for personal use without cost-of-sales adjustment
    • Aesthetic injectables VAT-exempt claimed without clearly therapeutic medical purpose
    • Mobile therapist vehicle personal-use under-declared
    • Apprentice or junior therapist mis-classified as self-employed

    Tax for cleaners

    • Cash-only domestic customer income under-declared (HMRC's most common cleaning audit area)
    • Agency-supplied 'self-employed' status when working pattern looks employed
    • Family help unpaid (becomes employment status issue if pattern is regular)
    • Capital vs revenue treatment of equipment upgrades
    • Vehicle business-use percentage under-declared for single-vehicle households
    • Cleaning products for personal home use claimed against business

    Tax for builders

    • Cash jobs not declared (especially on smaller domestic builds)
    • Failing to register as CIS contractor when first hiring a labour-only subbie
    • CIS deductions made but not paid over to HMRC by 22nd-of-following-month deadline
    • Subcontractors treated as 'self-employed' when HMRC's employment status indicator would say employed (employee + Employer NI risk)
    • Family member on payroll without genuine duties
    • Capital expenditure expensed (e.g. £15k mini-digger purchase booked as 'tools' on the P&L instead of capitalised + AIA-relieved)
    • Materials for own home extension claimed against business
    • VAT reverse charge applied incorrectly (or not at all when it should be)

    Tax for couriers

    • Personal car insurance + paid delivery work (insurance void; HMRC + insurer cross-referencing)
    • Parking penalties claimed as expense (NEVER allowable)
    • Mileage logs round-numbered or reconstructed after year end
    • Platform commission missed from gross-income calculation (declaring net only = under-declaring income)
    • Side hustle income not declared above £1,000 trading allowance
    • Tips not declared
    • Vehicle personal-use percentage under-declared for single-vehicle households

    Tax for creative freelancers

    • Foreign-currency income converted at exchange rates favourable to the taxpayer (HMRC uses spot rate on invoice/receipt date)
    • In-kind gifts from sponsors / brand collaborations not declared (Instagram + design industry common)
    • Capital vs revenue treatment of tablet/laptop upgrades
    • Subscribed software claimed for personal projects without apportionment
    • Spec work / unpaid pitches claimed as expense (no realised expense if you weren't paid)
    • Family member helping with admin without payroll arrangement
    • Home office percentage over-claimed

    Tax for dog groomers

    • Cash payments not declared (mobile grooming + retail salons both common cash trades)
    • Space-rental classification looking like disguised employment (commission split, salon-controlled bookings)
    • Family member helping out without payroll arrangement (employment status issue)
    • Initial Level 3 qualification claimed as expense (entry-to-trade, not allowable)
    • Personal use of mobile van (school run, weekend trips) under-declared
    • Products taken home for own dog without cost-of-sales adjustment
    • Council licensing fees claimed without holding the corresponding licence (some grooming-only setups don't require Animal Welfare Activities Licence)

    Tax for electricians

    • Cash domestic jobs not declared
    • Initial qualifying training (e.g. NVQ Level 3 in Electrical Installation) claimed as expense, NOT allowable as it's entry-to-trade
    • Family member salary at unrealistic rate (HMRC settlements scrutiny)
    • Van personal-use percentage under-declared
    • Materials for own home installation claimed against business
    • Test equipment repeatedly claimed without revenue growth
    • Solar PV / EV charger zero-rated VAT invoices without proper documentation of energy-saving-material category

    Tax for fitness instructors + personal trainers

    • Cash PT sessions under-declared
    • Gym 'rental' arrangements with commission-split looking like disguised employment
    • Online coaching + supplement affiliate income not declared
    • Family member helping out without payroll
    • Initial L2 + L3 PT qualifications claimed as expense (entry-to-trade, not allowable)
    • Music licensing not paid + not claimed
    • Mobile PT vehicle business-use percentage over-claimed

    Tax for florists

    • Cash sales not declared (HMRC's #1 florist audit area, walk-in retail is largely cash + card)
    • Spoilage write-off rates above 15% without supporting waste records
    • Stock for own/personal use (flowers for own home, family events) not adjusted out of cost of sale
    • Family members helping at peak times without payroll arrangement (employment status issue)
    • Wedding event-prop hire revenue not declared (treated as 'goodwill' or 'returned items')
    • Vehicle business-use percentage over-claimed (single-vehicle household)
    • Funeral director referral fees not declared as income (if received)

    Tax for food trucks + street food vendors

    • Cash sales not declared (street food + festivals are heavily cash-based; HMRC's #1 food truck audit area)
    • Hot/cold VAT split incorrectly applied (sandwiches kept in heated cabinet zero-rated when should be 20%)
    • Festival revenue share not declared (pitch percentage owed to organiser appearing as 'cost' rather than revenue)
    • Family member helping at events without payroll arrangement
    • Vehicle personal-use percentage over-claimed (occasional non-business trips not apportioned)
    • International 'research trips' claimed as wholly-business when largely personal
    • Pre-trading start-up costs claimed in years they were incurred rather than first trading year (pre-trading expenditure rules)

    Tax for gardeners

    • Cash domestic customer income not declared (most common audit area)
    • Capital vs revenue treatment of mower upgrades (HMRC challenges £2,000 mowers expensed instead of capitalised)
    • Family member helping out without payroll (becomes employment status issue)
    • Garden waste vehicle personal-use percentage under-declared
    • Materials for own garden claimed against business
    • Side-hustle income spanning £1,000 trading allowance threshold but not declared
    • Tree surgery initial NPTC qualifications claimed as expense (entry-to-trade, not allowable)

    Tax for hairdressers

    • Cash tips not declared (HMRC's #1 audit area for hairdressing)
    • Chair-renter mis-classification (salon owner risk: back PAYE + Employer NI)
    • Family member on salon payroll without genuine duties
    • Apprentice wages below minimum wage
    • Retail product stock taken for personal use, not adjusted out of cost-of-sales
    • VAT-registered salon failing to charge VAT on chair rent to chair renters (chair rent is standard-rated)
    • Mobile stylist's vehicle personal-use under-declared

    Tax for influencers + content creators

    • In-kind gifts not declared as trading income (HMRC's #1 creator-sector audit area)
    • Foreign-source income from US platforms under-declared
    • US tax withheld but no Foreign Tax Credit Relief claimed (over-paying UK tax)
    • Sponsorship paid via Wise/PayPal not declared (assumption that it's 'gift money')
    • Capital vs revenue treatment of camera + lens upgrades (£3k camera as 'revenue tools')
    • Personal travel claimed as business (the holiday-with-content-shot pattern)
    • Family members on payroll without genuine duties (HMRC settlements scrutiny)
    • OSS VAT not registered above €10,000 EU consumer digital sales

    Tax for consultants

    • Inside-IR35 status mis-classified as outside (HMRC enforcement target, consulting is the hottest sector)
    • 24-month rule breached (travel claimed for permanent workplace)
    • Spouse shares + dividends without commercial purpose
    • Director loan above £10,000 without BIK + s455 calculation
    • Conferences with token training that are essentially holidays
    • Subsistence claims without receipts
    • Pre-MBA / pre-qualification training claimed as expense (entry-to-trade)
    • Personal-purpose business travel claimed (e.g. family trip with one client meeting attached)

    Tax for mobile mechanics

    • Cash payments not declared (mobile + garage mechanics both heavily cash-based historically)
    • Stock for own/personal use (parts for own vehicle) not adjusted out of cost of sale
    • Initial Level 2/3 automotive qualification claimed as expense (entry-to-trade, not allowable)
    • Personal use of van not apportioned (school run, weekend trips)
    • Family member helping at the workshop without payroll arrangement
    • Scrap part sales (catalytic converters particularly) not declared as income
    • MOT failure-fix work not declared separately from MOT fee (HMRC's against DVSA MOT records)
    • Customer-site work pattern crossing 24-month rule without mileage adjustment

    Tax for photographers + videographers

    • Foreign-source income (stock library royalties, US clients) under-declared
    • US tax withheld but no Foreign Tax Credit Relief claimed (over-paying UK tax)
    • In-kind gifts from sponsors / brand collaborations not declared as income
    • Capital vs revenue treatment of equipment upgrades
    • Family member helping at weddings without payroll
    • Vehicle business-use percentage under-declared
    • Drone qualifications claimed as entry-to-trade training (not allowable)

    Tax for plumbers

    • Cash jobs not declared (HMRC Connect cross-references payment-platform data)
    • Family members on payroll without genuine duties (HMRC settlements legislation s.624 ITTOIA 2005)
    • Van personal-use percentage under-declared (BIK £4,020 not reported on P11D)
    • Tools repeatedly claimed as revenue expense without proportionate revenue growth
    • Materials purchased for personal household projects claimed against business
    • Repeated late filing of CIS monthly returns
    • VAT registration not triggered when rolling-12-month turnover crossed £90k

    Tax for landlords

    • Failing to declare BTL income at all (HMRC's Let Property Campaign disclosure facility exists for this)
    • Section 24 mortgage interest claimed as expense instead of basic-rate credit (incorrect, auto-reclassified)
    • Capital expenditure (e.g. new boiler installation) treated as repair (revenue) instead of capital
    • 60-day CGT reporting missed on residential disposal
    • Joint ownership split-share not properly declared via Form 17 + TR1
    • FHL claimed post-April-2025 abolition
    • Family member listed as joint owner without genuine beneficial ownership (HMRC anti-avoidance)
    • Repairs on properties between lets (vacancy period) not allowable

    Tax for side hustlers

    • Platform income above £1,000 not declared (HMRC Connect catches this routinely)
    • Personal item sales (Vinted/Depop) treated as trading when they're capital sales, opposite of usual problem
    • Multi-platform income aggregated incorrectly across SA years
    • Airbnb income treated as 'occasional' when frequency makes it a trade
    • Property allowance claimed simultaneously with Rent-a-Room scheme (mutually exclusive)
    • Trading allowance claimed PLUS actual expenses (mutually exclusive, choose one)
    • Side-hustle losses claimed against PAYE income without 'commercial trading' evidence
    • Foreign-source platform income under-declared (Patreon, Substack, foreign-routed OnlyFans)

    Tax for developers + IT contractors

    • Inside-IR35 status mis-classified as outside (HMRC enforcement target)
    • 24-month rule breached (travel claimed for permanent workplace)
    • Spouse shares + dividends without commercial purpose (HMRC settlements s.624)
    • Director loan account running above £10,000 without BIK + s455 calculation
    • Personal home internet 100% claimed (must apportion for personal use)
    • Conferences + training that are essentially holidays with token training (HMRC challenges)
    • Subsistence claimed without actual receipts (HMRC requires receipts for subsistence claims)
    • Pre-employment training claimed as expense (entry-to-trade, not allowable)

    Tax for tattoo artists

    • Cash deposits not banked (HMRC's #1 tattoo industry audit area)
    • Reported income inconsistent with booth-rent paid or social media booking activity
    • Convention income (UK + international) not declared
    • Foreign tax withheld but no Foreign Tax Credit Relief claimed
    • Booth-renter mis-classification (studio owner risk: back PAYE + Employer NI)
    • Initial apprenticeship training claimed as expense (entry-to-trade, not allowable)
    • Materials for own (artist's) tattoos claimed against business

    Tax for taxi + PHV drivers

    • Personal car insurance + paid passenger work (insurance void; HMRC + insurer cross-referencing)
    • Cash fares not declared (HMRC's #1 taxi audit area despite card-payment shift)
    • Platform commission missed from gross-income calculation (declaring net only = under-declaring income)
    • Mileage logs round-numbered or reconstructed after year end
    • Parking penalties claimed as expense (NEVER allowable)
    • Personal use of taxi vehicle (school run, weekend trips) not apportioned
    • Initial Knowledge of London / licensing claimed as expense (pre-trading expenditure within 7-year window may be defensible; entry-to-trade strictly NOT allowable)
    • Tips received in cash not declared

    Underlying statutes

    The legislative anchors behind the triggers above. Each is verified against legislation.gov.uk and gov.uk guidance current at the last-reviewed date.

    Digital platforms must report seller income to HMRC under the UK implementation of the OECD model reporting rules. (Finance Act 2023 s 349 + The Platform Operators (Due Diligence and Reporting Requirements) Regulations 2023 (SI 2023/817))

    Self Assessment late-filing penalties: £100 fixed at day 1, then daily £10 from day 90, then tax-geared bolt-ons at 6 and 12 months. (FA 2009 Sch 55)

    MTD ITSA mandation thresholds and commencement set by regulation under primary powers in F(No.2)A 2017. (F(No.2)A 2017 Sch A1 + The Income Tax (Digital Requirements) Regulations 2021 (SI 2021/1076) as amended)

    Behaviour-based penalty bands (careless / deliberate / deliberate-and-concealed) determine penalty range after an enquiry; unprompted disclosure reduces the band. (FA 2007 Sch 24)

    Last reviewed: